Advances in the art of preparing block copolymers (from two or more monomers) with clearly defined block lengths and narrowly defined controlled molecular weight (mol wt), substantially free from homopolymer residues, has provided the bases for a host of commercially significant polymers prepared by anionic polymerization. Such advances in the art of preparing block copolymers, it is generally acknowledged, are not known in the art of cationic ring-opening polymerization. With respect even to the general art of cationic polymerization, Prof. Joseph Kennedy said "Cationic polymerizations have only very recently emerged from the dark middle ages and reached the point where systematic tailoring of polymer structures became possible." (see Isotopics, pg 4, May 1982).
Specifically with respect to the cationic polymerization of ethylene oxide with SnCl.sub.4, Worsfold and Eastham found that each SnCl.sub.4 molecule rapidly initiates two polymer chains which slowly increase in length through stepwise addition of monomer. They observed that addition of monomer does not regenerate the reaction, and assumed termination to involve no transfer but rather destruction of the catalyst. See High Polymers, Vol. XIII, Part I, Polyalkylene Oxides and Other Polyethers, by Norman G. Gaylord, pg 113-114, Interscience Publishers, John Wiley & Sons, New York (1963). Thus, it would appear that there was a specific suggestion that block copolymers would not be formed by a living polymerization reaction with an acid catalyst or initiator, if the monomer had an ethylene oxide structure. By "living polymerization" I refer to one which is, for all practical purposes, free from transfer and termination reactions.
To one skilled in the art, the synthesis of polymers by cationic ring-opening polymerization and an assessment of the properties of block copolymers based on their structure, is bedded in theoretical considerations, which have been formulated with less conviction than those related to non-ring-opening cationic polymerizations, generally. An assessment of the probability that a little-understood process will provide a block copolymer with any particular structure and desirable properties such as stability, controllable block lengths and mol wt distributions, is even more theory-oriented, if not speculative.
Such theoretical considerations as the effect of reactivity ratios of monomers from which individual blocks of a particular block copolymer are formed, even if these ratios are determined in an analogous cationic polymerization system, is of no known relevance either with respect to the ease of formation of the particular block copolymers of my invention, or the particularity of their properties as a result of being derived by a specific cationic ring-opening polymerization.
The difficulty of tailoring block copolymers by cationic ring-opening polymerization so as to provide a mol wt within a narrow range and well-defined functionality is well known. Recently, novel block and graft copolymers based on the di- and multicationically ended living polyacetals and polyethers have been shown to be formed without a hydroxyl-containing material, and under anhydrous conditions. See Cationic Ring-Opening Polymerization, by Stanislaw Penczek, Polish Academy of Sciences, Center of Molecular and Macromolecular Studies, 90-362 Lodz, Poland; see Makromol. Chem., Suppl., 3, 17-39 (1979). This work appears to confirm the teachings of the Dreyfuss U.S. Pat. No. 3,850,856 that OH groups would `kill` the system, if it was a living one.
In view of the foregoing teachings, one unacquainted with the theory is more likely to consider the results of certain steps in a polymerization process quite easily accounted for, at least after the fact, than one who is more closely acquainted with the theory. Further, one skilled in the art would expect that properties of block copolymers will be different from those of random copolymers, but the difference in properties between certain block copolymers which superficially appear to be similar, may have a wholly different significance from differences in apparently similar random copolymers.
This invention is particularly directed to a process for making certain branched block copolymers, and linear block copolymers (all of which are herein referred to as `block copolymers` for reasons which will presently be evident), using a hydroxyl-containing organic material (hereinafter "HCM", for brevity) as the chain propagator which furnishes OH groups as chain propagation sites; and, using preselected HCMs, for making graft, star and comb block copolymers; and, which process, relies upon a living polymerization generated by the catalytic action of a fluorinated acid catalyst having the formula HMF.sub.6 wherein M is selected from phosphorus, arsenic and antimony; or, an oxonium salt of the acid. The process of my invention yields block copolymers which persons skilled in the art believed could not be made before the discovery of my process.
More specifically, the block copolymers of my invention are made by a living cationic ring-opening polymerization, and propagated at sites furnished by the HCM in the presence of a known catalyst disclosed in U.S. Pat. No. 3,585,227, and in U.S. Pat. No. 3,850,856, the disclosures of which are incorporated by reference herein as if fully set forth. The polymerization disclosed in the U.S. Pat. No. 3,850,856 was based on water, or ethylene glycol terminating the growing polymer chains by introducing OH groups at the terminal positions. This polymerization is now discovered to be a living polymerization which is quite surprising since it is well known that "The nature of the processes involved in cationic copolymerisations of monomer mixtures, and the experimental limitations which they impose, have made this synthetic route to block copolymers generally unsatisfactory, at least for most comonomer pairs." (see Block Copolymers, by Allport, D. C. and Janes, W. H., pg 354, John Wiley & Sons, 1973). Implicitly, this corroborates a prejudice against cationic living polymerization systems.
Further, since known polymers such as those described in the '856 patent are clearly stated to be hydroxyl-ended, the use of a HCM as a chain propagator which furnishes hydroxyl (OH) groups as chain propagation sites, was deemed to have been precluded. Thus, there was no motivation to explore the possibility that, even a hydroxyl-ended prepolymer might function as a chain propagator in the same manner as the HCM. Nevertheless, it has now been found that, under certain conditions, growth of block copolymers is propagated with a HCM, which growth occurs in a well-definable living polymerization system. More particularly, it now appears that the structure of the residue of the HCM chain propagator, whether monomeric or polymeric, of low molecular weight or high, does not adversely affect the growth of a block copolymer, but generates a living system able to grow preselected blocks, so that the overall polymer weight, the polymer segmental weight, and the polymer's functionality are each narrowly defined.
Epihalohydrin polymers formed by cationic polymerization with triethyloxonium hexafluorophosphate (TEOP) are known to be formed as disclosed in U.S. Pat. No. 3,850,857. However, neither the molecular weight of the polymers nor their functionality can be narrowly controlled, resulting in the loss of control of the polymers' properties. In contrast, the unexpectedly close control of molecular weight and functionality of the block copolymers of my invention facilitates the production of a variety of tailored block copolymers which are not only useful as film-formers, viscosity increasing agents, dispersing agents for polymerization, and the like, but also for mineral beneficiation where highly specific properties are essential to the making of sharp, and hence profitable, separations.
Such close control of mol wt and functionality is only possible because of the unqiue characteristics of a living polymerization found to be the key to the process, in which the mol wt of the polymer is increased directly with the amount of monomer converted to polymer.
Some two decades ago, it was known that hydroxyl group-containing compounds are condensed with epoxyalkyl halides in the presence of fluoboric catalysts as disclosed in U.S. Pat. No. 3,129,232. Soon thereafter it was shown in U.S. Pat. No. 3,305,565 that water is an initiator in the presence of various acid catalysts forming halo-hydroxyl terminated polymers which could be epoxidized. More recently, terminally unsaturated liquid epihalohydrin polymers have been disclosed in U.S. Pat. No. 4,256,910 which are relatively low in molecular weight, in which polymers a backbone is obtained by homopolymerizing an epihalohydrin, or forming random copolymers by copolymerizing two or more epihalohydrins, or copolymerizing an epihalohydrin with a vicinal epoxide, and using the same TEOP catalyst as used in the '856 process. It is clear that this teaching of combinations of a wide variety of monomeric alkylene ethers with an epihalohydrin refers to random copolymers and fails to indicate that a block copolymer might be formed under yet-to-be specified conditions. Neither is there any indication that the hydroxyalkyl(meth)acrylate used in the '910 patent functioned as a chain propagator, nor that the mol wt and functionality of the polymer were narrowly defined.
U.K. Patent Application No. 2,021,606A teaches that hydroxyl-terminated poly(chloroalkylene ethers) have not proven entirely satisfactory when prepared by cationic ring-opening polymerization as disclosed in U.S. Pat. Nos. 3,850,856; 3,910,878; 3,910,879; and, 3,980,579. Thus, the problems inherent in the use of prior art catalysts referred to in the foregoing U.S. patents have been documented. A solution to the problems was provided in the British patent application. This solution was to use a catalyst comprising (i) a fluorinated acid catalyst having the formula H.sub.m XF.sub.n+m wherein X is selected from boron, phosphorus, arsenic and antimony, m is 0 or 1 and n is 3 when X is boron and n is 5 when X is phosphorus, arsenic and antimony, and, (ii) a polyvalent tin compound.
This British patent teaches that only tin fluorometallic compounds even among other Group IV metals, has a peculiar catalytic action not attributable to Group V fluorometallic compounds. The British catalyst permits water to provide hydroxyl-terminated polymers with the same structure as those polymers provided by other HCMs. No distinction is made between HCMs in which the residue is other than H, and one in which it is H (as it is when the HCM is water). It is disclosed that, with the specified tin fluorometallic compounds, the resulting polymers include random copolymers, and certain block copolymers. Whatever the mechanism of the polymerization reaction, it is clear that the difference in the overall polymer formed in the British invention is attributable to its use of a specific catalyst, namely, a fluorinated acid-polyvalent tin compound catalyst, rather than (say) the trialkyloxonium hexafluoro(Group V) metal, used in the '856 patent, and now found to be useful in the instant invention.
The quaternization ("amination") of polyepihalohydrins is known to yield highly water soluble products useful as coagulants, for example in the treatment of raw sewage, as disclosed in U.S. Pat. No. 3,591,520. However, as is well known, the amination of poly(epichlorohydrin) "PECH" does not proceed very easily, even under elevated pressure and temperature, with the result that only partial amination is generally achieved. Accordingly, it might be expected that a block copolymer having a glycidyl ether segment would not be easily aminated because of the solubility properties of the block copolymer. Thus it is quite unexpected that reactive halogens in a block copolymer of (i) a HCM, (ii) a polyepihalohydrin, and, (iii) at least one poly(glycidyl ether), should be substantially fully aminated, if so desired, despite the presence of segments which clearly do not lend themselves to amination in any known manner.